According to the development of information communication technique, two-way communication through a packet switched network such as IP (Internet Protocol) network has been performed actively.
Especially, in these years, a technique of an IP phone using a function of VoIP (Voice over IP) has been prevalent. In the technique of the IP phone using the function of VoIP (Voice over IP), sound data is packetized and the packetized sound data is transmitted between a plurality of terminals through the packet switched network. This enables voice call through the Internet. Further, the IP phone may reduce the cost that would be necessary for the facilities and management of the typical so-called fixed phone network and reduce a basic charge and a call charge more than heretofore.
The quality of the communication, however, becomes unstable unlike the typical fixed phone network, because of passing through the Internet. A business provider supplying the IP phone service has to monitor and control the communication quality in order to ensure a certain communication quality. Taking into consideration that the communication amount of the IP phone calls is increasing more and more, it is required that the communication quality is monitored more accurately.
As the typical method for measuring the quality of a call, the following one is proposed. According to the method described in Japanese Patent Application Laid-Open No. 2005-286900, respective measuring devices are set at a plurality of points on a network. The measuring device measures a state of the communication at a point, based on the packet information about communication packets passing through the point where the measuring device is set, and transmits the measurement result to a collecting device, correspondingly to the measuring device identifying information for identifying the above measuring device and the communication identifying information for identifying the measured communication. The collecting device analyzes the communication quality based on the communication state information and the measuring device identifying information corresponding to the communication identifying information transmitted from the respective measuring devices.
According to the method described in Japanese Patent Application Laid-Open No. 2008-113186, a QoS routing device, which is a node of a logic network for transmitting the data transmitted between the user terminals checks whether the received data is specific data or not, forwards the data, measures each communication quality value of each link connected to its own device according to the flow of the specific data, to require the measurement accuracy of the communication quality value for every link, and assigns the number of the flows of the specific data at higher ratio to the link with the less measurement accuracy.
As an index indicating the communication quality, there is the loss rate of packets. For measuring the loss rate of the packets, it is necessary to capture a packet by some method. There are a passive method and an active method mainly as the method for capturing a packet. According to the passive method, the measuring device is set on a network and the packet flowing in the network is captured. According to the active method, two terminals for test are prepared. One terminal transmits a packet through the network and the other terminal receives the packet.